Vertical linearity in television receivers



Jah. 22, 1952 E CLARK 2,583,323

VERTICAL LINEARITY 1N TELEVISION RECEIVER FiledMarch 29, 1949 SYNC. SEPA/MIUR mvo #MR .5y/Nc. DEE

Inven'orzf fdl/W?? V5/ A i' www Patented Jan. 22, 1952 UNITI-ao STATES PATENT oFFlc'sv Y VRII TLSO Edwinv L. Clark, Collingswood, N; Jg assignortol Radio Corporation of America, a corporationv of. Delaware Application March 29, 1949, Serial No; 84,024

i (c1. 32o- 1)A Claims; l This invention relates '.ttzrsignal` 'generator-stand more particularly to methods and sawtoothwave generators'. ItA is well known that. when a constant direct voltage is suddenly applied to a condenser' and` resistor in series, the transient voltage acrossV the condenser increases atan exponential ratei and thatl it is sufficiently linear during the first part ci.l the charging cycle. to beuseful' in sweepcircuits used in conjunction with-cathode ray tubes; In. such circuits, therefore; the vdirect voltage re. quired must be of' thev order ofziour times themaximum voltage. attained by' the condenser'.v This. obviously results in ineicient operation. The eiiiciency of generators such as deflection generators in: television: systems is, of course. quiteimportant.

. Accordingy tothis: invention, the-voltage across:-

the'. charging condenser of a'saw tooth increases at alinear rate approachingthe directY voltage applied. This is accomplished by'distorting the exponential voltageY wavev across the condeI-iseill and feeding the distorted wave into series with: the steady direct' Voltage applied to the condenser in such manner that the resultant voltage applied across; thev condenser is lower at the beginning ofiv the charging cyclethan at the end. In other words, the difference*betweenthe'voltage applied. to the condenser. and the condenser voltage that opposes it is substantially constant throughout the charging cycles. ItV will therefore. be seen that the. magnitude: ofLthe: supplyvoltag'e redu'ired'isv less` than that useddn. the standard sweep circuits for a given linear change in voltage across the condenser.

Accordingly. it is an object of this invention to provide a means for linearly charging a condenser.

It is a further object of this invention to provide a means whereby a condenser may be charged at a linear rate to a voltage approaching the charging voltage.

Another object of this invention is to provide a circuit for generating a linear sweep voltage wave with a minimum of direct current potential.

A still further object of this invention is to increase the linearity of the output of a sweep generator with the addition of a minimum number of component parts.

These and other objects will become apparent from a detailed consideration of the drawing in which:

Figure 1 shows a sweep circuit embodying one form of this invention.

Figure 2 shows the waveform developed by the integrating circuit, and

Figure 3 shows the waveform developed` by. the differentiating circuit.

Since the rateA at which av condenser charges isY determinedv by the resistance in `series with itzan'd the resultant Voltage applied, it ordinarily charges at an exponential rate,-fbut if the ,api pliedavoltage is maintained at a constant value,A the rate of charge is determined solely by the value of the series resistor. According to this inventiontherefore,. there is not only applied a steady value off direct currentpotential to the resistorand condenser in series, but there is also inserted. in series with the condenser a source of. direct potential the value of which: is varied during the'- charging cycle so as tornaintain the resultant voltage applied to thecondenser at a constant level.Y This controlled potential opposes the. steady direc-t potential at all times buthis reduced as the condenser charges so that the chargingv potential isA constant. In other. words theI voltage across the controlled. source of potential` and the condenser does not change during the charging cycle.V d Y,

This desired variationvin the charging Voltage is obtained by sucessivelyintegrating and differentiating. the voltageA developed across the condenserv and inserting the differentiated voltage series with the steady direct potential'. 1n order that the differentiated wave not be of the same shapef as the original wave. it is necessary that the time constants of.V the diirtati'gl and integrating. circuitsbe different. I

uIn. Figure. 1'- there is shown ablock diagram' oi' a standard televisin receiver; wherein the output of sync separator 2"is fed to the grid 4l of the discharge tube 6 via the primary 8 of transformer I0, coupling condenser l2 and Variable resistor I4, the latter being connected between the grid 4 and ground so that the duration of the sweep voltage Wave can be adjusted. The plate IS of discharge tube 6 is connected to B+ via the secondary I8 of transformer In and a load resistor 22, and the output appearing at the junction 24 of the resistor and the secondary I8 is coupled via condenser 26 and grid leak resistor 28 to the grid 3 of the sweep voltage output amplifier 32, the plate 62 being connected to B-lvia the primary 36 of output transformer 38.

The charging condenser across which the desired voltage waveform is to be developed before being applied to grid 30 is indicated by numeral 40 and is connected between junction 24 and ground via a peaking resistor 42, the cathode 44 of ampliiier 32 and the parallel resistance 46 and condenser 48. Inasmuch as the cathode 58 of the discharge tube 6 is grounded and its plate I6 is connected to junction 24, it rapidly discharges the condenser 40 when a pulse from sync separator 2 biases it into conduction.

Thus the circuit described is a standard sweep generator in which condenser 40 is charged and discharged so as to form a voltage wave similar to that indicated by numeral 56, provided the condenser is charged to a fraction of the B+' potential. By addition of the integrating cire cuit comprised of resistor 58 and condenser 60 between the plate 62 and cathode 44 an output such as shown in Figure 2 is developed across the condenser 60, and this is supplied to a'diierentiating circuit comprised of condenser 63 and vseries with said source of voltage, means for peaking resistor 42 so as to produce a waveform such as shown in Figure 3 across the resistor 42.

Because resistor 42 is connected between groundv and one plate of condenser 40, the voltage of that plate varies with respect to ground as shown in Figure 3, and the charging voltage actually applied to the condenser is seen to be maintained substantially constant for as condenser 40 charges the voltage of the plate decreases. Therefore, in accordance with the theory explained above, a linear sweep voltage is generated having a maximum amplitude at a value approaching B+. It is to be noted that this desired result is obtained by the addition of only two condensers and a resistor to a standard circuit.

It is believed that the method of feeding back the voltage developed across a charging condenser via successive integrating and differenperiodicallyrdischarging said condenser, polarity reversing means, said latter means having its input connected so as to receive the voltage developedacross said resistor, an integrating circuit connected to the output of said polarity reverser, a differentiating circuit connected to the output of said` integrating circuit, and the if input being connected so as to receive a voltage tiating circuits of different time constants into f proportional to the current passing through said condenser, an integrating circuit having input and output terminals, the input terminal of said integrating circuit being connected to the output terminal of said -polarity'reversing means, a differentiating circuit having input and output terminals, the input terminal of said differentiating circuit being connected to the output terminal of said integrating circuit, and means for apply- 'f ing the voltage appearing at the output terminal the voltage developed across said resistance. and means for introducing the diierentiated voltage into series relationship with said condenser. 2. The method of charging a condenser through a resistance in such manner that the voltage l Number Name Date 2,126,243 Busse et al Aug. 9, 1938 2,383,333

Milward Aug. 21, 1945 

